Symbiosis is a mutually beneficial interaction between two organisms. Most plants are symbiotic with fungi (Petrini, 1986) and these fungi play important roles in the structure, function, and health of plant communities (Bacon and Hill, 1996; Clay and Holah, 1999; Petrini, 1986; Read, 1999; Rodriguez and Redman, 1997).
It has been demonstrated that a symbiotic relationship between plants and fungi can confer enhanced growth to host plants. For example, strains of endophytic fungi have conferred tolerance to host plants to extreme environmental conditions including high temperature, drought, and high salt content (Redman et al., 2002; Rodriguez et al., 2004; Rodriguez and Redman, 2008a; Rodriguez et al., 2009). In addition to promoting stress tolerance, endophytes also increase nutrient acquisition and growth rates of host plants, and enhance water use efficiency (Rodriguez et al., 2008; Rodriguez et al., 2009).
Trichoderma harzianum (T. harzianum) is a fungal species that encompasses a wide variety of physiologically specialized strains. Certain strains are used as biocontrol agents against soil-borne diseases of plants, and others are used for industrial production of cell wall degrading enzymes (Naseby et al., 2000). Trichoderma harzianum has been shown to induce metabolic changes in plants that increase their resistance to a wide variety of plant-pathogenic microorganisms and viruses (Harman et al., 2004). It has previously been shown that T-22, a particular strain of Trichoderma harzianum, can increase the growth of plant and root development under some conditions. T-22 can also solubilize plant nutrients for plant uptake that would otherwise be unavailable to plants in certain soils (Altomare et al., 1999; Harman et al., 2004).
Abiotic stress involves the negative impact of physical and chemical factors on living organisms such as temperature, water, pH, and nutrient limitation. Promoting plant growth in conditions of marginal to extreme abiotic stress would allow plants to become established in non-ideal environments, creating new vegetation. Creating new vegetation is important to soil remediation of polluted sites created by modern industry, agriculture, and other human activities.
The Athabasca oil sands in Alberta, Canada are the second largest in the world after Saudi Arabia. Oil sands contain bitumen, a semisolid mixture of complex hydrocarbons derived from coal or petroleum (Oil Sands Discovery Center, 2006) that are converted into synthetic crude oil. Oil sand surface-mining is damaging to the environment as it involves removal of trees and animals, and use of local water. About three cubic meters of liquid and solid tailings are produced per barrel of oil extracted. Current daily production from the oil sands, estimated at 1.5million barrels (240,000 cubic meters), would cover 100 football fields about knee-deep in tailing sands (TS). Since 1967, TS already cover more than 50 square kilometers to a far greater depth. The rate of extraction is forecast to double by 2020 and triple by 2030, See the world wide web at (.energy,gov.ab.ca/OilSands/oilsands.asp).
Tailing sands, the solid by-product of oil sand extraction, contain polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs), which inhibit water absorption. Additionally, the oil extraction process removes much of the minerals and would also kill any soil microflora existed within the oil sands. This leaves the tailing sands deficient in minerals and flora. Thus, the tailing sands are challenging to support the plant life necessary to reclaim the sites.
Oil companies are expending considerable effort to overcome the challenges associated with tailings disposal and ultimate site reclamation (Matt Price, 2008). Traditional remediation methods of tailing sands are costly and time consuming. The cost of remediation per hectare now averages about $30,000 and it will take 15 years to remediate.
Compared to traditional methods (mixed fertilizer with plant material removed prior to surface mining, and stockpiled) bioremediation appears to be less labour intensive, and more environmentally safe since the tailing sand does not have to be covered with peat or other plant material, that must be taken from elsewhere. According to the reclaim standard, a reclaimed growing medium should be able to support a healthy plant community (similar to that of a comparable natural area) (Bois et al., 2006). Developing new vegetation on tailing sands is the key to a successful remediation.